The miniaturization of semiconductor circuit elements has reached a point where feature sizes of about 10 nm are fabricated on a commercial scale. As the dimensions continue to get smaller, new challenges arise for process steps like filling a gap between circuit elements with a dielectric material that avoids electrical cross-talk. As the width between the elements continues to shrink, the gap between them often gets taller and narrower, making the gap difficult to fill without the dielectric material getting stuck to create voids or weak seams. Conventional chemical vapor deposition (CVD) techniques often experience an overgrowth of material at the top of the gap before it has been completely filled. This can create a void or seam in the gap where the depositing dielectric material has been prematurely cut off by the overgrowth; a problem sometimes referred to as breadloafing.
One solution to the breadloafing problem has been to use liquid precursors for the dielectric starting materials that more easily flow into the gaps. A technique currently in commercial use for doing this is called spin-on-glass (SOG). More recently, techniques have been developed that impart flowable characteristics to dielectric materials deposited by CVD. These techniques can deposit flowable precursors to fill a tall, narrow gap with porous material while reducing an incidence of creating voids or weak seams. While the new flowable CVD techniques represent a significant breakthrough in filling tall, narrow (i.e., high-aspect ratio) gaps with porous materials (such as low-k dielectric materials), there is still a need to increase the density of the gapfill material.